MEASUREMENTS OF THE COSMOLOGICAL PARAMETERS OMEGA AND LAMBDA FROM THEFIRST 7 SUPERNOVAE AT Z-GREATER-THAN-OR-EQUAL-TO-0.35

We have developed a technique to systematically discover and study hig h-redshift supernovae that can be used to measure the cosmological par ameters. We report here results based on the initial seven of more tha n 28 supernovae discovered to date in the high-redshift supernova sear ch of the Supernova Cosmology Project. We find an observational disper sion in peak magnitudes of sigma(MB)=0.27; this dispersion narrows to sigma(MB,corr)=0.19 after ''correcting'' the magnitudes using the ligh t-curve ''width-luminosity'' relation found for nearby (z less than or equal to 0.1) Type Ia supernovae from the Calan/Tololo survey (Hamuy et al.). Comparing light-curve width-corrected magnitudes as a functio n of redshift of our distant (z=0.35-0.46) supernovae to those of near by Type Ia supernovae yields a global measurement of the mass density, Omega(M)=0.88(-0.60)(+0.69) for a Lambda = 0 cosmology. For a spatial ly flat universe (i.e., Omega(M) + Omega(Lambda) = 1), we find Omega=0 .94(-0.28)(+0.34) or, equivalently, a measurement of the cosmological constant, Omega(Lambda) = 0.06(-0.34)(+0.28) (<0.51 at the 95% confide nce level). For the more general Friedmann-Lemaitre cosmologies with i ndependent Omega(M) and Omega(Lambda), the results are presented as a confidence region on the Omega(M)-Omega(Lambda) plane. This region doe s not correspond to a unique value of the deceleration parameter q(0). We present analyses and checks for statistical and systematic errors and also show that our results do not depend on the specifics of the w idth-luminosity correction. The results for Omega(Lambda)-versus-Omega (M) are inconsistent with Lambda-dominated, low-density, flat cosmolog ies that have been proposed to reconcile the ages of globular cluster stars with higher Hubble constant values.